If I can add my observations as a porty user.
A couple of years ago, I saw a new Prochem Blazer being demo'd and was very impressed with it's performance. But I felt that it was VERY NOISY.
Last year, I saw Dave Roelant's immaculate but well used Boxxer 421 in use and, apart from the impressive performance, was amazed at how quiet it's 21hp B&S unit was. Would I be correct to presume that the 18hp B&S of the 318 would be equally quiet?
Safe and happy cleaning
Ken